Terminal devices, such as smart phones, tablet-type personal computers (PCs), or the like, that are widely used in recent years are mainly small and thin types because the terminal devices are assumed to be carried. Consequently, such a terminal device generally has a small number of external interfaces that are mounted on the device main body. Thus, if an external interface is additionally installed, the terminal device is generally used by connecting the terminal device to a function expansion device, such as a cradle, a docking station, or the like. In the following, a description will be given by using a docking station as an example of the function expansion device.
Furthermore, some docking stations have built-in batteries. By allowing an electric power supply to be supplied from the battery on the docking station side to a terminal device that is connected, even if an AC adapter is not used, it is possible to reduce consumption of the battery of the terminal device and thus it is possible to attempt to use the terminal device for a longer time.
In general, charging of a battery is performed by, using a dedicated charger integrated circuit (IC) and an embedded controller (EC) that controls the charger IC, collectively judging an electric power supply situation of the system, an amount of electric power consumption, the battery state, or the like. In a system in which a battery is mounted on both the terminal device and the docking station, a charger IC and an embedded controller are generally mounted on both the terminal device and the docking station. Furthermore, charging of each of the batteries is performed by the surplus electric power obtained by subtracting the electric power that is used for the operation of the system from an amount of the rated electric power of the AC adapter.
When each of the charger ICs of the batteries of the main body and the battery of the DS individually proceeds to perform the charging, by mutually grasping an electric power situation of the counterpart, the two batteries can efficiently be charged within an amount of the rated electric power of the AC adapter. In general, the AC adapter that is used for a tablet or the like has a small outer shape and an amount of rated electric power thereof is small by taking into consideration of portability. Consequently, if a priority is given to an electric power supply with respect to charging of a battery of a terminal device, the electric power that can be used to charge the battery of the docking station becomes very small. In this state, the time taken to complete the charging of the battery of the docking station may possibly become very long.
As a technology to efficiently allocate electric power in an amount of rated electric power of an AC adapter, there is a conventional technology that changes electric power of charging of each battery while monitoring the electric power consumed in an AC adapter connected to a docking station and giving a priority for surplus electric power to the charging of each battery of a terminal device.
Furthermore, as a technology that charges two batteries, there is a conventional technology that arranges a charging device, which includes therein a spare battery between an external power supply and an electronic device that includes therein a battery, and that controls the charging of each of the batteries in accordance with an electric power state of an electronic device.
Patent Document 1: Japanese Laid-open Patent Publication No. 2009-301281
Patent Document 2: Japanese Laid-open Patent Publication No. 08-251830
However, in a charging device that includes therein the spare battery, attaching/detaching of the terminal device with respect to an apparatus that includes therein a battery is not considered; therefore, it is difficult to efficiently charge both the batteries of the docking station and the terminal device that can be attached and detached.
Furthermore, the conventional technology that monitors electric power consumption of the AC adapter monitors the electric power consumption of the AC adapter connected to the docking station by performing communication between the embedded controller of the terminal device and the embedded controller of the docking station. Consequently, a problem occurs when a large amount of electric power received from the AC adapter that is performing the charging of the following battery is instantaneously consumed. For example, a problem occurs when, in a state in which a terminal device is connected to a docking station, a load applied to the terminal device or the docking station is sharply increased. Furthermore, a problem occurs when, if a battery of a docking station to which the terminal device is not connected is being charged by using a large amount of electric power, a terminal device that is in a high load state is connected. In such a situation, because a large amount of electric power is instantaneously consumed from the AC adapter, electric power that exceeds an amount of rated electric power of the AC adapter may possibly be output from the AC adapter, while electric power that is used to charge a battery due to communication between the embedded controllers is being decreased. Consequently, the AC adapter becomes deteriorated and a supply of power from the AC adapter may possibly stop. Furthermore, with the conventional technology that monitors the electric power consumption of the AC adapter, because the AC adapter is connected to the docking station, it is difficult to handle the state in which the AC adapter is connected to the terminal device.